RNAV approach glidepath capture
An RNAV approach may provide an FMS-generated glidepath. A magenta line on the map alone does not tell you that the final vertical mode is armed or captured.
Read PTH and GP as different vertical modes. PTH follows the FMS descent path. FSS says VNAV observes the selected altitude; monitor the actual level-off and take control if it does not occur as expected. For an approach with vertical guidance, FSS describes GP as the final glidepath mode. Only after GP is captured does the documented procedure call for setting the missed-approach altitude; do not make that change just because GP is armed. FSS vertical modes [38] · PTH and GP discussion [158].
If GP remains armed when you expect it to capture, check the approach, active leg, altitude, path and FMA. Do not assume that an aircraft following a plausible slope has captured GP. Stabilise and use the missed approach if the required guidance or a safe approach cannot be maintained.
For its RNAV, LPV and LNAV/VNAV procedures, FSS calls for FMS navigation and says not to use green APP/LOC guidance. Check the navigation source and the FMA before arming the approach. FSS procedure guide [9].
Select the exact approach
Choose the published RNAV procedure and the transition required by the clearance. Inspect the active legs and the missed approach.
Confirm the source
Select FMS guidance. Check that the navigation source and magenta needles on the PFD match the approach briefing.
Review the constraints
Compare final approach fixes, altitudes and speed restrictions with the chart. Check that performance data is complete.
Set up the intercept
Fly the cleared path and altitude. Stabilise the aircraft before concentrating on the final capture.
Arm approach guidance
For the FSS RNAV example, select FMS as the navigation source and confirm that the approach is in the active flight plan and LNAV and VNAV are active. Within 30 NM, with LOC preview off, press APP. For an approach with vertical guidance, FSS describes an armed L/VNAV or LPV indication.
Confirm capture
GP capture must be observed on the FMA.
For an RNAV procedure with vertical guidance, FSS describes GP as the captured glidepath mode. Verify that the displayed guidance and actual path agree.
Set missed altitude
After GP capture, FSS says ALTSEL can be set to the missed-approach altitude. Monitor the path and be ready to go around. [157] [9]